The present invention relates to a tone generator, and more particularly to an electronic tone generator.
As shown in FIG. 1, a known electronic monotone generator includes a memory 101 for storing tone (frequency) and time data of each generated note, an address counter 102 for applying an address signal to memory 101 so that the tone information stored at a plurality of addresses in memory 101 can be read out successively, a high-frequency oscillator 103 outputting clock pulses to be divided down by a programmable counter 104 according to the data related to the musical note stored in memory 101, a wave-shaping circuit 105 which converts the selected frequency signal outputted by programmable counter 104, gives it a selected wave form and applies a desired modulating envelope to the signal, an amplifier 106 amplifying the shaped signal wave form, an electroacoustic transducer 107 converting the output of amplifier 106 to an acoustic music sound and another programmable counter 108 dividing clock pulses supplied from another oscillator 109. The division ratio of programmable counter 108 is variable in response to the time data stored in memory 101. Since the music produced by such an electronic tone generator is inferior to that produced by a mechanical music box and the sound quality produced thereby is of monotone quality, a Japanese patentee, Kabushiki Kaisha Suwa Seikosha, has sought patenting an electronic tone generator bearing U.S. Pat. No. 4,273,019 which makes an improvement over the above described electronic monotone generator in that not only it is capable of producing music that compares in tonal quality with a good mechanical tone generator, but also the good tonal quality can be combined with the advantages of electronic circuitry in allowing reprogramming of the melody and the elimination of cumbersome mechanical parts, such as a winding spring.
As shown in FIG. 2A, the patented electronic tone generator includes at least two musical note producing circuits 201, 202 which are the same as the note producing circuit 110 of FIG. 1, a mixing amplifier 203 combining and amplifying the signal wave forms produced by circuits 201, 202, an electroacoustic transducer 204 converting the amplified signal into a musical sound and two oscillator 208, 209 for note and timing signals respectively serving note producing circuits 201, 202 to further simplify the construction. As one of the disclosed examples in the patent, first musical note producing circuit 201 produces notes of a desired melody and if we designate the audio frequency of the music note produced by circuit 201 as f, then second note producing circuit 202 can be adapted to produce a note having an audio frequency of f.+-..DELTA.f so that a beat frequency is introduced into the music sound. The more detailed block diagram of FIG. 2A is shown in FIG. 2B which corresponds to FIG. 9 in the above mentioned patent. Further information relating to FIG. 2B, if desired, can be obtained from the patent the contents of which are incorporated herein for reference purpose.
Although the patented electronic tone generator has achieved the objects that it produces more acoustically pleasing music and music with special sound effect, one note may be produced concurrently with the sounding of another note, successive notes in the same melody can overlap in sound, output signals can include a beat frequency or an echo effect and it can simultaneously play two independent melodies, one melody having special sound effects, it still has the following disadvantages:
(1) Each note producing circuit 201 (202) has its own memory 402 (402'). One of memories 402, 402' stores tone and time data for the notes of a main melody while the other one stores data for the notes of an accompanying melody. It is quite possible, however, that the number of notes for a main melody (accompanying melody) is larger than that for an accompanying melody (main melody) and therefore it often results in that both memories 402, 402' cannot be fully utilized and are wasted to some extent.
(2) Each producing circuit 201 (202) has its own circuit means 403', 406 (403, 406'). It is tried by the present inventor to use a common circuit for two or more note producing circuits.
The inventor attempts to overcome the shortcomings encountered by the patented electronic tone generator while maintaining all the advantages it represents.